1. Field of the Invention
The invention relates to a control pilot valve apparatus for use in, for example, conduits carrying a sensed fluid to shift an operating valve from one position to another position.
2. Description of the Prior Art
There are many pilot assemblies available for use in safety systems for monitoring a flow line pressure and sending a signal to or removing a signal from an end device, such as a safety valve, or a control console.
The most common pilot assembly employed is known as a spool pilot that employs a spool valve and a sensing piston opposed by an adjustable coil spring. For example, when the pressure of the fluid being sensed by the piston overcomes the force of the associated spring, the flow of control fluid through the spool valve is altered to control flow within a conduit. It will be appreciated that in such systems, the coil spring assembly generally must be guided to minimize friction. The systems are typically only 88 to 90% accurate with respect to repeatability of the trip point of the associated valving arrangements. Presently, government regulations require such systems to be much more accurate in their sensing properties, particularly with respect to repeatability.
There are spool pilot assemblies which are able to meet the present higher accuracy requirements, but are deemed to be commercially very expensive.
Bourdon tube assemblies are also used for sensing flow line pressures and monitoring the same. However, these assemblies have limited over-pressure capacities. If the Bourdon tube assemblies are used to sense systems at a pressure of 1500 psi, the maximum limiting pressure may be 2,000 psi. This is not very satisfactory when the system is employed in connection with sensing a flowing well which typically operates at a pressure of 2,000 psi, and, then when the well is shut in, the pressure may rise to 5,000 psi, considerably above the capacity of the monitoring system.
It is an object of the invention to provide a sensing system which is inexpensive to produce and has a substantial range of sensitivity and a high overpressure capacity.
Another object of the invention is to provide a fluid pressure pilot assembly having low sensing frictional characteristics.
Another object of the invention is to provide a fluid pressure pilot assembly exhibiting a high motion amplification capability.
Another object of the invention is to provide a fluid pressure pilot assembly wherein the primary spring biasing force is removed from the motion amplification system.
Another object of the invention is to provide a pressure fluid pilot assembly employing a cantilevered spring member which is stable, inherently self-guided, and may be guided through its movement with minimal frictional contact.